To be perfectly honest, I was so pleased to remember about Long v. Ballantine that I stopped reading at that point and came here to post.

With that said, I don't see how Ars later characterizes the clip as anything but fair use. Looking specifically at

The Romney ad seems like as clear-cut a case of fair use as can be imagined. Obama's singing is a core part of the ad's message, and copyright law explicitly mentions commentary and criticism as justifications for fair use. And it's hard to imagine the ad harming the market for Al Green CDs or iTunes tracks.

Ars seems to be saying that the ad meets two of the criteria for fair use: that it is commentary or criticism, and that it has no effect on the work's market. How does this strike you as indicating that they are rejecting fair use?